metamorphic
Iron-rich metamorphic rock, likely banded iron formation fragment
Hematite–magnetite-rich quartzite (BIF); Fe₂O₃/Fe₃O₄ with SiO₂
AI-generated identification · may be incorrectDark brown to black, rusty weathering, metallic to earthy luster, granular texture, and possible thin quartz banding. Hardness about 5.5–6.5; hematite may leave a red-brown streak, while magnetite is strongly magnetic; cleavage is absent or poor.
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Physical properties
Dark brown to black, rusty weathering, metallic to earthy luster, granular texture, and possible thin quartz banding. Hardness about 5.5–6.5; hematite may leave a red-brown streak, while magnetite is strongly magnetic; cleavage is absent or poor.
Formation & geological history
Formed when silica-rich chemical sediments and iron oxides precipitated from ancient oceans, then lithified and metamorphosed. Most banded iron formations formed roughly 2.5–1.8 billion years ago during the Precambrian oxygenation of Earth’s atmosphere.
Uses & applications
Important iron ore when sufficiently rich; otherwise used as an educational or lapidary specimen and collected for its metallic appearance.
Geological facts
Rust-colored patches commonly represent limonite/goethite formed by weathering. A magnet test and streak test can distinguish magnetite-rich material from hematite-rich material.
Field identification & locations
Common in iron-rich terrains such as the Lake Superior region, Western Australia, Brazil, India, and South Africa. The specimen’s identity is provisional from the image; test magnetism, streak, and hardness for confirmation.
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